Wrinkles increase as a phenomenon of skin aging with increasing age, and from a cosmetic viewpoint there is highly increasing interest in preventing and improving wrinkles, especially in women. Wrinkles are largely classified as fine wrinkles formed as a result of reduced function of the epidermis including the stratum corneum, and large wrinkles (or “expression wrinkles”) formed by reduced function of the dermis below the epidermis. Wrinkles formed by reduced function of the epidermis including the stratum corneum are caused primarily due to reduction in the moisture-retaining function of the epidermis as a result of aging, ultraviolet rays, low temperature, low humidity and the like. Wrinkles formed by reduced function of the dermis, on the other hand, are caused by increase in matrix metalloproteases (MMPs) as a result of aging and ultraviolet rays, as well as mechanical stress, leading to collapse of the elastic structure of the skin composed of collagen and elastin (PTL 1 and NPLs 1, 2 and 3). It is known that fine wrinkle grooves formed in the skin progress to large wrinkles by deeply carving the grooves (NPL 4), and therefore fine wrinkles and large wrinkles are intimately related with each other.
The fact that fine wrinkles tend to be formed in cold, dry climates has become commonly recognized by most people, and for prevention and amelioration of fine wrinkles, it is considered important to promote moisture retention by cosmetics, and especially cosmetic water, latexes, creams, essences and the like, as well as to increase humidification using humidifiers. Cosmetics, and particularly cosmetics containing humectants such as glycerin and hyaluronic acid, are used to promote moisture retention.
In the prior art, there have been known methods of screening for candidate substances that increase stratum corneum transparency by means of skin roughening models using dry epidermis (PTL 2), and methods of screening for candidate substances that improve or increase skin barrier function, by using changes in the structure of stratum corneum intercellular lipids as a measure (PTL 3). Such methods are used to screen for candidate substances that improve stratum corneum transparency and skin barrier function, but there has been no description of screening for candidate substances that ameliorate wrinkles.